The present invention relates to electric toothbrushes, and more particularly to an electric toothbrush which has an overload protection.
U.S. Pat. No. 5,289,604 discloses all electric toothbrush, as shown in FIG. 1. The electric toothbrush 10 comprises a handle section 1 and a brush section 2. The handle section 1 houses a battery 11, an electric motor 12, a drive shaft 13, and a translating device 14 for converting the continuous rotary motion of the electric motor 12 into a rotary motion reversing direction in alternating sequence for driving the drive shaft 13. The brush section 2 comprises a hollow mounting tube 23 receiving a brush shaft 22. Arranged at the end of the brush section 2 is a bristle supporting structure 21 for receiving bristles. The bristle supporting structure 21 has a bevel gear 24 meshed with a bevel gear 26 at the front end of the brush shaft 22. The mounting tube 23 and the brush shaft 22 are adapted to be connected to the handle section 1 by coupling means 25. When the bristles are damaged or worn away with use, the brush section 2 can be conveniently detached from the handle section 1 for a replacement. Locking structure is needed for locating the brush section relative to the handle section in an axial and a radial direction with respect to a longitudinal center line of the brush shaft. This structure of an electric toothbrush has certain drawbacks. Because the bristle supporting structure is turned back and forth at a speed of about 2,800 rpm., when an excessive pressure is applied to the bristles against the teeth, the teeth may be easily damaged. Therefore, electric toothbrush manufacturers commonly instruct the users not to apply much pressure on the bristles against the teeth. Furthermore, dentists do not recommend that children use electric toothbrushes because electric toothbrushes may damage growing children's teeth.
Because conventional electric toothbrushes lave no means to protect against overload, electric toothbrush users may apply a high enough pressure to the bristles against the teeth, causing damage to the teeth.